One option that might be worth considering is replacing the furnace with a boiler and water-to-air coil/air handler. I've heated my last two houses with EFM's and think they're great, but there are a few considerations here that to me seem to weigh in favor of a boiler. First, while the EFM furnace uses the same stoker as a 520 boiler, EFM recommends against operating it over 7 teeth of feed in the furnace, so the furnace is limited relative to the boiler in the btu's it can generate. Furnaces in general don't make DHW very effectively compared to boilers, so the limited output of the furnace is even more significant if you're trying to produce DHW. Also, especially in an old house like that, a boiler provides flexibility for adding a zone to heat the garage, basement, cold room, etc. that isn't easily achieved with hot air. Even just running the boiler with the jacket off can function as effective radiant heat for your basement if needed (worked very well in our old 1890 house). Finally, I don't think EFM offers an oil package for their stoker furnace, and I don't think there are many others who do.
Overall, I'd suggest taking a good look at boiler-based options that could tie into your hot air system, while also providing efficient generation of DHW. Relative to the furnace, a 520 can provide more btu's for heat, can generate 5 gpm of DHW indefinitely and is available with or without oil backup.